I was on another forum and ran across this info. For those that may be interested in a double hitch trailer and want to build your own, and make have it cheaper, this is interesting. This is for one of those trailers that have a double swivel wheel so it doesn't affect the backing up with double hitch.
Heres the site
http://www.doublehitch.com/
Posting moved per OPs request - CRAFT-Guy